linux-kernel - Re: [PATCH 5/6] arm64: dts: renesas: r9a08g045: Add TSU node

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Message-ID: <034707dd-e6b1-4a39-860b-b972fa438645@linaro.org>
Date: Thu, 30 Jan 2025 18:53:57 +0100
From: Daniel Lezcano <daniel.lezcano@...aro.org>
To: Claudiu <claudiu.beznea@...on.dev>, rafael@...nel.org,
 rui.zhang@...el.com, lukasz.luba@....com, robh@...nel.org,
 krzk+dt@...nel.org, conor+dt@...nel.org, geert+renesas@...der.be,
 magnus.damm@...il.com, mturquette@...libre.com, sboyd@...nel.org,
 p.zabel@...gutronix.de, ulf.hansson@...aro.org
Cc: linux-pm@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-clk@...r.kernel.org,
 Claudiu Beznea <claudiu.beznea.uj@...renesas.com>,
 Biju Das <biju.das.jz@...renesas.com>
Subject: Re: [PATCH 5/6] arm64: dts: renesas: r9a08g045: Add TSU node

On 03/01/2025 17:38, Claudiu wrote:
> From: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
> 
> Add TSU node along with thermal zones and keep it enabled in the SoC DTSI.
> The temperature reported by the TSU can only be read through channel 8 of
> the ADC. Therefore, enable the ADC by default.
> 
> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
> ---
>   arch/arm64/boot/dts/renesas/r9a08g045.dtsi    | 43 ++++++++++++++++++-
>   .../boot/dts/renesas/rzg3s-smarc-som.dtsi     |  4 --
>   2 files changed, 42 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/boot/dts/renesas/r9a08g045.dtsi b/arch/arm64/boot/dts/renesas/r9a08g045.dtsi
> index a9b98db9ef95..fd74138198a8 100644
> --- a/arch/arm64/boot/dts/renesas/r9a08g045.dtsi
> +++ b/arch/arm64/boot/dts/renesas/r9a08g045.dtsi
> @@ -205,7 +205,6 @@ adc: adc@...58000 {
>   			#address-cells = <1>;
>   			#size-cells = <0>;
>   			#io-channel-cells = <1>;
> -			status = "disabled";
>   
>   			channel@0 {
>   				reg = <0>;
> @@ -244,6 +243,17 @@ channel@8 {
>   			};
>   		};
>   
> +		tsu: thermal@...59000 {
> +			compatible = "renesas,r9a08g045-tsu";
> +			reg = <0 0x10059000 0 0x1000>;
> +			clocks = <&cpg CPG_MOD R9A08G045_TSU_PCLK>;
> +			resets = <&cpg R9A08G045_TSU_PRESETN>;
> +			power-domains = <&cpg>;
> +			#thermal-sensor-cells = <0>;
> +			io-channels = <&adc 8>;
> +			io-channel-names = "tsu";
> +		};
> +
>   		vbattb: clock-controller@...5c000 {
>   			compatible = "renesas,r9a08g045-vbattb";
>   			reg = <0 0x1005c000 0 0x1000>;
> @@ -690,6 +700,37 @@ timer {
>   				  "hyp-virt";
>   	};
>   
> +	thermal-zones {
> +		cpu_thermal: cpu-thermal {
> +			polling-delay-passive = <250>;
> +			polling-delay = <1000>;
> +			thermal-sensors = <&tsu>;
> +			sustainable-power = <423>;
> +
> +			cooling-maps {
> +				map0 {
> +					trip = <&target>;
> +					cooling-device = <&cpu0 0 2>;
> +					contribution = <1024>;
> +				};
> +			};
> +
> +			trips {
> +				sensor_crit: sensor-crit {
> +					temperature = <125000>;
> +					hysteresis = <1000>;
> +					type = "critical";
> +				};
> +
> +				target: trip-point {
> +					temperature = <100000>;
> +					hysteresis = <1000>;
> +					type = "passive";
> +				};

1. As you specified the sustainable power, the power allocator would be 
used. However, it needs an intermediate passive trip point before 
reaching the mitigation because the governor has to collect data ahead 
of the passive mitigation trip point in order to feed the PID loop. This 
trip point is not bound to any cooling device

2. The mitigation temperature is set to 100°C. The MTBF decay factor of 
the semi-conductor will be increased by more the 100x times during the 
thermal episodes stress thus reducing its lifespan considerably if it 
hits this temperature often (but I doubt with a single Cortex-A55).

3. It would make sense to add a 'hot' trip point so the user space can 
take an action to reduce the thermal pressure before reaching the 
critical temperature

4. IIUC, the CPU does not do voltage scaling but only frequency scaling, 
right ? If it is the case, then it is even more true that the mitigation 
trip point should be reduced because the frequency scaling only may not 
suffice to provide a cooling effect


> +			};
> +		};
> +	};
> +
>   	vbattb_xtal: vbattb-xtal {
>   		compatible = "fixed-clock";
>   		#clock-cells = <0>;
> diff --git a/arch/arm64/boot/dts/renesas/rzg3s-smarc-som.dtsi b/arch/arm64/boot/dts/renesas/rzg3s-smarc-som.dtsi
> index ef12c1c462a7..041d256d7b79 100644
> --- a/arch/arm64/boot/dts/renesas/rzg3s-smarc-som.dtsi
> +++ b/arch/arm64/boot/dts/renesas/rzg3s-smarc-som.dtsi
> @@ -102,10 +102,6 @@ x3_clk: x3-clock {
>   	};
>   };
>   
> -&adc {
> -	status = "okay";
> -};
> -
>   #if SW_CONFIG3 == SW_ON
>   &eth0 {
>   	pinctrl-0 = <&eth0_pins>;


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